Recently, researchers in Shanghai Institute of Optics and Fine Mechanics (SIOM), Chinese Academy of Sciences (CAS), carried out a systematic investigation on the broadband nonlinear photoresponse and ultrafast carrier dynamics from ultraviolet to near-infrared of 2D palladium diselenide (PdSe₂). The related research results have been published in Advanced Optical Materials on Oct. 22, 2021.

PdSe₂ is regarded as a promising material to bridge the gap between graphene and MoS₂ because of its bandgap varying from 1.3 eV (monolayer) to 0 eV (bulk), which has the potential for application in next-generation optoelectronic devices. Scientists observed the steady-state and transient photoresponse of trilayer PdSe₂ films by the usage of nonlinear optical technique and ultrafast carrier dynamics system. Trilayer PdSe₂ exhibits broadband nonlinear absorption behavior in the ultraviolet, visible, and near-infrared regions. Especially, PdSe₂ exhibits well-performed saturable absorption at 346 nm and 520 nm, which indicates that PdSe₂ can be used as a saturable absorber in ultrafast short-wavelength lasers.

Furthermore, based on its high modulation depth, a PdSe₂-based visible light thresholder is proposed, whose function is to extract an undetectable pulse signal drowned in strong stochastic noise and thereby improve the signal-to-noise ratio. Pump-probe technique, along with transient absorption spectra, reveal the recombination lifetime of photo-generated carriers is approximately 100 ps, and the intrinsic recombination mechanism includes shallow defects-assisted Auger scattering and deep defects-assisted trap saturation.

This work proves that PdSe₂ has the broadband optical response, the high modulation depth, and the fast response speed, which implies that PdSe₂ is a promising material in broadband nano-optoelectronic devices.

Figure 1. Broadband nonlinear absorption and transient absorption spectra of PdSe2. (Image by SIOM)